Flame-resistant polyurea foam

ABSTRACT

The flame-resistant polyurea foam of the invention contains calcium sulfate dihydrate as filler and ammonium polyphosphate as flame retardant. Its bulk density is from 25 to 250 kg/m 3  and the number of open cells is above 80% of all its cells. The polyurea has been formed from a reaction of prepolymers of diphenylmethane 4,4&#39;-diisocyanate with water. 
     The polyurea foam of the invention can be used as a block foam or on-site foam for sound and/or heat insulation.

The invention relates to flame-resistant polyurea foam, a process forits production and its use.

DE 39 09 083 C1 discloses a gypsum foam having a porous structure,containing a polyurea, which has a bulk density of from 100 to 400kg/m³, is open-celled and contains as polyurea the condensation productof diphenylmethane 4,4'-diisocyanate prepolymers and water. The gypsumfoam is to be used as sound and/or heat insulation.

A disadvantage of this process is hydraulically setting calcium sulfatehemihydrate (α-calcium sulfate; CaSO₄.1/2H₂ O) is to be used as startingmaterial, because the preparation of the latter by dehydration ofcalcium sulfate dihydrate requires considerable amounts of energy. Inthe subsequent processing of the prior art (DE 39 09 083 C1, Examples 1and 2), gypsum materials having a bulk density of above 1000 kg/m³ areobtained, so that the bulk density region of less than 100 kg/m³ (=<0.1g/cm³) which is of interest for the most important application sector(heat insulation, acoustics) is not achieved. In addition, suchmaterials cannot be used for the application area of sound absorption,since no cell structure is present. Likewise, there are no indicationsas to whether, and, if so, how the gypsum "foams" described can be madeflame-resistant, which is an indispensable prerequisite for their use asbuilding materials for heat insulation and sound absorption. The processindicated would be difficult to transfer to the industrial scale, sincethe mixtures obtained according to the prior art (DE 39 09 083 C1,Examples 1 and 2) have a mortar-like consistency.

Surprisingly, these problems can be solved by, according to theinvention, starting out from calcium sulfate dihydrate, by usingrelatively large amounts of water and prepolymers of diphenylmethane4,4'-diisocyanate to ensure that the mixtures of the starting componentsare pumpable or castable and by using ammonium polyphosphate as flameretardant.

Thus, addition of ammonium polyphosphate made it possible to produceopen-celled and light (bulk density: <100 kg/m³) polyurea foams whichmet the requirements of the German Building Material Class DIN 4102-B2if the bulk density was above 35 kg/m³ and the proportion of gypsum wasover 30% by mass.

Furthermore, it was possible for the first time, by addition of ammoniumpolyphosphate, to produce open-celled, light (bulk density: <100 kg/m³)and fire-resistant polyurea foams which met the requirements of theGerman Building Material Class DIN 4102-B1. This was surprising and notforeseeable because with falling bulk density the proportion ofnoncombustible inorganic filler has to be reduced and the proportion ofcombustible polyurea has to be increased to the same extent.

A very important side effect of the use of ammonium polyphosphate asflame retardant is the better binding of the gypsum into the polyureafoam. While a gypsum-filled polyurea foam which has been producedwithout use of ammonium polyphosphate forms a great deal of dust duringprocessing with partial loss of the pulverulent gypsum, in the polyureafoams of the invention the dusting is suppressed even when only smallamounts of ammonium polyphosphate are used.

A BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the X-ray analysis of gypsum according to this invention.

FIG. 2 shows the X-ray analysis of another type of gypsum according tothis invention.

FIG. 3 shows the X-ray analysis of plaster of paris according to thisinvention.

FIG. 4 shows thermogravimetric analysis of gypsum according to thisinvention.

FIG. 5 shows thermogravimetric analysis of another type gypsum accordingto this invention.

FIG. 6 shows thermogravimetric analysis of plaster of paris according tothis invention.

FIG. 7 illustrates an apparatus used in the preparation of polyurea foamaccording to this invention.

In detail, the invention now provides a flame-resistant polyurea foamwhich

- contains calcium sulfate dihydrate,

- contains, as flame retardant, ammonium polyphosphate, if desired incombination with further halogen-free flame retardants and/orhalogen-free synergists,

- has a bulk density of from 25 to 250 kg/m³,

- has a number of open cells which is above 80% of all its cells,

- comprises polyurea which has been formed from a reaction ofprepolymers of diphenylmethane 4,4'-diisocyanate with water.

The polyurea foam of the invention can furthermore, preferably and asdesired,

1. contain calcium sulfate dihydrate in the form of natural gypsum orchemical gypsum (e.g. from flue gas desulfurization of power stations);

2. contain, as flame retardant, a free-flowing, pulverulent ammoniumpolyphosphate of the formula (NH₄ PO₃)_(n) having n=20 to 1000,preferably from 500 to 1000, which is sparingly soluble in water;

3. have the ammonium polyphosphate microencapsulated and contain from0.5 to 25% by mass of a water-insoluble, if desired cured, syntheticresin which encloses the individual ammonium polyphosphate particles;

4. have a bulk density of from 35 to 90 kg/m³ ;

5. have the following composition (% by mass):

a) from 15 to 70%, preferably from 20 to 60%, of polyurea,

b) from 25 to 80%, preferably from 30 to 70%, of calcium sulfatedihydrate,

c) from 1 to 15%, preferably from 2 to 10%, of flame retardant,

and, if desired,

d) from 0.1 to 5%, preferably from 0.2 to 2%, of fibrous fillers,

e) from 0.1 to 2% of catalysts based on nitrogen compounds for theisocyanate/water reaction,

f) from 0.1 to 2% of foam stabilizers based on polysiloxanes,

g) from 0.01 to 2% by weight of auxiliaries for dispersion and/orsuspension and/or making thixotropic.

The invention further provides a process for producing the new polyureafoam, which comprises mixing calcium sulfate dihydrate, flame retardant,prepolymers of diphenylmethane 4,4'-diisocyanate, water and, if desired,fibrous fillers, catalysts, foam stabilizers and also dispersants and/orsuspending agents and/or thixotropes, with the foaming proceeding as aresult of the formation of carbon dioxide, and bringing the cured foamto a residual moisture content of below 2%.

The process step of the invention for removing the moisture of thefiller-containing polyurea foam is indispensable, since the polyureafoam obtained after the foaming reaction is complete has the nature of asoft foam which is only lost as a result of the drying step in which aweight loss of 20-30% occurs. With this drying step, the polyurea foamtakes on a rigid foam structure having corresponding mechanical strengthvalues.

The fibrous fillers serve to improve the mechanical strength of thepolyurea foam; inorganic (e.g. glass fibers) or organic (e.g. cellulosefibers from waste-paper) fiber materials can be used.

A preferred embodiment of the process of the invention can furthercomprise mixing

from 15 to 60% by mass of calcium sulfate dihydrate,

from 15 to 45% by mass of prepolymers of diphenylmethane4,4'-diisocyanate,

from 25 to 50% by mass of water,

from 0.5 to 10% by mass of flame retardant,

and, if desired,

from 0.1 to 5% by mass of fibrous fillers,

from 0.1 to 2% by mass of catalysts based on nitrogen compounds for theisocyanate/water reaction,

from 0.1 to 2% by mass of foam stabilizers based on polysiloxanes and

from 0.01 to 2% by mass of dispersants and/or suspending agents and/orthixotropes.

Finally, the invention provides for the use of the new polyurea foam asblock foam or on-site foam for sound and/or heat insulation.

Said block foam serves, for example, for the production of acousticboards, heat insulation boards, composite boards or shaped parts, forexample insulation shells produced by milling machining for pipes orapparatus, or as granular insulation material for loose beds.

EXAMPLES

In the following examples, the following starting materials were used:

- Calcium sulfate dihydrate (flue gas desulfurization gypsum F)

Use was made of gypsum from the flue gas desulfurization plant of theFrauenaurach power station, which had a mean particle size of 0.030 mmand whose X-ray analysis (see FIG. 1) indicated that it was calciumsulfate dihydrate containing at most 1% of calcium sulfate hemihydrateor calcium sulfate anhydrite. This also confirms the thermogravimetricanalysis (see FIG. 4).

- Calcium sulfate dihydrate (flue gas desulfurization gypsum H)

Use was made of gypsum from the flue gas desulfurization plant of theHeilbronn power station, which had a mean particle size of 0.028 mm andwhose X-ray analysis (see FIG. 2) indicated that it was calcium sulfatedihydrate containing at most 1% of calcium sulfate hemihydrate orcalcium sulfate anhydrite. This also confirms the thermogravimetricanalysis (see FIG. 5).

- Calcium sulfate hemihydrate

Stucco plaster from Gebr. Knauf, Neuss works, whose X-ray analysis (seeFIG. 3) indicated that it was calcium sulfate hemihydrate having lowcontents of calcium sulfate dihydrate and calcium sulfate anhydrite.This also confirms the thermogravimetric analysis (see FIG. 6).

- ®Sapogenat T-040 (Hoechst AG, Frankfurt/Main)

This tributylphenol polyglycol ether (containing 4 mol of ethyleneoxide) is a liquid having a density of 0.97 g/ml (at 50° C.) and aviscosity of 40-60 mPa.s (at 50° C.).

- ®Hostaflam AP 462 (Hoechst AG, Frankfurt/Main)

A microencapsulated long-chain ammonium polyphosphate (NH₄ PO₃)_(n),n=about 1000! as a fine white powder having extremely low solubility inwater.

- ®Elastan 8009 (Elastogran GmbH, Lemfoerde)

A prepolymer of diphenylmethane 4,4'-diisocyanate having an NCO contentof 16.4% and a viscosity at 25° C. of about 5000 mPa.s.

EXAMPLE 1 (COMPARISON)

In a 2 1 stirred vessel, 175 g of flue gas desulfurization gypsum F, 35g of ®Hostaflam AP 462 and 11 g of a 2% strength solution of acommercial suspending agent based on a high molecular weightpolysaccharide were stirred into 280 ml of water and, after sufficienthomogenization, were mixed with 350 g of ®Elastan 8009. After a stirringtime of 1-2 minutes (at 1500-2000 rpm), the mixture was poured into anopen wooden mold having the dimensions 20 cm×20 cm×40 cm. After afurther reaction time of about 2 hours, the foam block was taken fromthe wooden mold and stored for 24 hours at room temperature. The bulkdensity of the moist foam block (after removal of the external skin) was52 kg/m³ ; after drying to constant weight at 60° C., the value fell to40 kg/m³. The test pieces for the small burner test in accordance withDIN 53438, part 2, were sawn therefrom in the rise direction and, priorto the fire test, were stored for 48 hours in the standard environmentin accordance with DIN 50014-23/50-2. The fire test was carried out ontest specimens having a thickness of 13 mm.

The test results are summarized in Table 1.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        31%              by mass of calcium sulfate dihydrate                         6%               by mass of ® Hostaflam AP 462                            63%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

EXAMPLE 2 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 52.5 g of ®HostaflamAP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        30%              by mass of calcium sulfate dihydrate                         9%               by mass of ® Hostaflam AP 462                            61%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 3 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 70 g of ®Hostaflam AP462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        29%              by mass of calcium sulfate dihydrate                         12%              by mass of ® Hostaflam AP 462                            59%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 4 (COMPARISON)

The procedure of Example 1 was repeated, but using 350 ml of water, 210g of flue gas desulfurization gypsum F and 26.25 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        36%              by mass of calcium sulfate dihydrate                         5%               by mass of ® Hostaflam AP 462                            59%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 5 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 350 ml of water, 210g of flue gas desulfurization gypsum and 35 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        35%              by mass of calcium sulfate dihydrate                         6%               by mass of ® Hostaflam AP 462                            59%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 6 (COMPARISON)

The procedure of Example 1 was repeated, but using 400 ml of water, 245g of flue gas desulfurization gypsum F and 26.25 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        40%              by mass of calcium sulfate dihydrate                         4%               by mass of ® Hostaflam AP 462                            56%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 7 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 400 ml of water, 245g of flue gas desulfurization gypsum F and 35 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        39%              by mass of calcium sulfate dihydrate                         6%               by mass of ® Hostaflam AP 462                            55%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 8 (COMPARISON)

The procedure of Example 1 was repeated, but using 450 ml of water, 280g of flue gas desulfurization gypsum F and 8.75 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        44%              by mass of calcium sulfate dihydrate                         1%               by mass of ® Hostaflam AP 462                            55%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 9 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 450 ml of water, 280g of flue gas desulfurization gypsum F and 17.5 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        43%              by mass of calcium sulfate dihydrate                         3%               by mass of ® Hostaflam AP 462                            54%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 10 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 450 ml of water, 350g of flue gas desulfurization gypsum F and 8.75 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        50%              by mass of calcium sulfate dihydrate                         1%               by mass of ® Hostaflam AP 462                            49%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 11 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 450 ml of water, 350g of flue gas desulfurization gypsum F and 17.5 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        49%              by mass of calcium sulfate dihydrate                         2%               by mass of ® Hostaflam AP 462                            49%              by mass of polyurea                                          <0.1%            by mass of polysaccharide                                    ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 12 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 450 ml of water, 350g of flue gas desulfurization gypsum F and 17.5 g of ®Hostaflam AP 462and 2 g of cellulose fibers.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        49%          by mass of calcium sulfate dihydrate                              2%          by mass of ® Hostaflam AP 462                                48%          by mass of polyurea                                              0.3%         by mass of cellulose fibers                                      <0.1%        by mass of polysaccharide                                        ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 13 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 450 ml of water, 385g of flue gas desulfurization gypsum F and 8.75 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        52%          by mass of calcium sulfate dihydrate                              1%          by mass of ® Hostaflam AP 462                                47%          by mass of polyurea                                              <0.1%        by mass of polysaccharide                                        ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 14 (ACCORDING TO THE INVENTION)

The procedure of Example 1 was repeated, but using 450 ml of water, 420g of flue gas desulfurization gypsum F and 8.75 g of ®Hostaflam AP 462.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        54%          by mass of calcium sulfate dihydrate                              1%          by mass of ® Hostaflam AP 462                                45%          by mass of polyurea                                              <0.1%        by mass of polysaccharide                                        ______________________________________                                    

The test results are summarized in Table 1.

EXAMPLE 15 (ACCORDING TO THE INVENTION)

In a plant schematically shown in FIG. 7,

    ______________________________________                                        90 kg        of flue gas desulfurization gypsum F                             11 kg        of ® Hostaflam AP 462                                        35 kg        of ® Elastan 8009                                            60 kg        of water                                                         ______________________________________                                    

were mixed at room temperature and introduced into a closed, nongastightsteel mold having the dimensions 1.6 m×1.0 m×1.0 m, with a foamformation process commencing after a few minutes as a result of theformation of carbon dioxide. After the foaming process was complete, thesolid block obtained was sawn into slices having a thickness of about 50mm, these being dried at about 60° C. in a stream of warm air.

The following values were determined on the foam plates which had a bulkdensity of 79.9 kg/m³ :

    ______________________________________                                        Oxygen index   (ASTM-D2863)  0.41                                             Thermal conductivity                                                                         (DIN 52612)   0.048 W/m · K                           Open cell content                                                                            (ASTM-D2856/87)                                                                             98.3%                                            ______________________________________                                    

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        66%          by mass of calcium sulfate dihydrate                              8%          by mass of ® Hostaflam AP 462                                26%          by mass of polyurea.                                             ______________________________________                                    

The test results obtained in the fire resistance test in accordance withDIN 4102 are summarized in Table 2.

EXAMPLE 16 (ACCORDING TO THE INVENTION)

The procedure of Example 14 was repeated, but using the followingstarting materials:

    ______________________________________                                        90 kg    of flue gas desulfurization gypsum F                                 11 kg    of ® Hostaflam AP 462                                            35 kg    of ® Elastan 8009                                                65 kg    of water in which 45 g of a commercial suspending                             agent based on a high molecular weight poly-                                  saccharide had been dissolved.                                       ______________________________________                                    

Test specimens for the fire resistance test in accordance with DIN 4102were sawn from the dried, 49 mm thick foam plates which had a bulkdensity of 89.6 kg/m³, and these were stored to constant weight in thestandard environment (DIN 50014-23/50-2).

The test results are summarized in Table 2.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        66%          by mass of calcium sulfate dihydrate                              8%          by mass of ® Hostaflam AP 462                                26%          by mass of polyurea                                              <0.1%        by mass of polysaccharide                                        ______________________________________                                    

EXAMPLE 17 (ACCORDING TO THE INVENTION)

The procedure of Example 14 was repeated, but using the followingstarting materials:

    ______________________________________                                        90 kg        of flue gas desulfurization gypsum H                             11 kg        of ® Hostaflam AP 462                                        36 kg        of ® Elastan 8009                                            65 kg        of water                                                         ______________________________________                                    

Test specimens for the fire resistance test in accordance with DIN 4102were sawn from the dried, 48 mm thick foam plates which had a bulkdensity of 85.6 kg/m³, and these were stored to constant weight in thestandard environment (DIN 50014-23/50-2).

The test results are summarized in Table 2.

The gypsum-filled polyurea foam had the following composition:

    ______________________________________                                        66%          by mass of calcium sulfate dihydrate                              8%          by mass of ® Hostaflam AP 462                                26%          by mass of polyurea.                                             ______________________________________                                    

EXAMPLE 18 (COMPARISON)

In DE 39 09 083 C1,"gypsum foam having a porous structure, process forits production and its use", it is stated in column 3, lines 47-50 that"as gypsum in the present invention, all neutral or weakly acid,hydraulically setting calcium sulfate modifications . . . can be used".In repeating the Examples 1 and 2, the following was found:

* When 360 g of stucco plaster, 89.3 g of water, 89.3 g of ®Elastan 8009and 2.4 g of ®Sapogenat T-040 were mixed as described in Example 1, nofoaming process was observed and a gray-white, stone-like product wasobtained, this having no porous structure.

After a storage time of 24 hours at room temperature, the product had abulk density of 1190 kg/m³. After drying to constant weight at 60° C., abulk density of 1125 kg/m³ was found.

Note: The drying is a process step which is not provided for in DE 39 09083.!

* When 360 g of stucco plaster, 119.2 g of water, 72.4 g of ®Elastan8009 and 2.4 g of ®Sapogenat T-040 were mixed as described in Example 2,no foaming process was observed and a gray-white, stone-like product waslikewise obtained, this having no porous structure. After a storage timeof 24 hours at room temperature, a bulk density of 1030 kg/m³ wasmeasured, which fell to 930 kg/m³ after drying to constant weight at 60°C.

To ensure that the non-usability of calcium sulfate hemihydrate is notrestricted to the mixing ratios of the Examples 1 and 2, furtherexperiments were carried out using a higher amount of water and alsousing an increased amount of water and an increased amount of isocyanateprepolymer.

* using a method similar to Example 2, doubled amount of water

When 360 g of stucco plaster, 238.4 g of water, 72.4 g of ®Elastan 8009and 2.4 g of ®Sapogenat T-040 were mixed, no foaming process wasobserved and a gray-white, stone-like product was obtained, this havingno porous structure.

After a storage time of 24 hours at room temperature, a bulk density of1280 kg/m³ was determined, which fell to 970 kg/m³ after drying toconstant weight at 60° C.

* using a method similar to Example 2, a quadrupled amount of water

When 360 g of stucco plaster, 476.8 g of water, 72.4 g of ®Elastan 8009and 2.4 g of ®Sapogenat T-040 were mixed, no foaming process wasobserved and a gray-white, stone-like product was obtained, this havingvirtually no porous structure.

After a storage time of 24 hours at room temperature, the bulk densitywas 1120 kg/m³ which fell to 620 kg/m³ after drying to constant weightat 60° C.

* using a method similar to Example 2, doubled amount of water, doubledamount of isocyanate prepolymer

When 360 g of stucco plaster, 238.4 g of water, 144.8 g of ®Elastan 8009and 2.4 g of ®Sapogenat T-040 were mixed, no foaming process wasobserved and a gray-white, stone-like product was obtained, this havingonly a weakly pronounced, porous structure. After a storage time of 24hours at room temperature, the bulk density was 660 kg/m³ which fell to470 kg/m³ after drying to constant weight at 60° C.

As can be seen from the above comparative examples, in no case weregypsum foams having a bulk density of from 100 to 400 kg/m³ able to beproduced. Therefore, the statements of DE-C 39 09 083 that hydraulicallysetting calcium sulfate modifications can be used and that bulk densityranges from 100 to 400 kg/m³ (corresponds to from 0.1 to 0.4 g/cm³) canbe achieved and also that the gypsum foam of the invention isopen-celled, are not accurate.

An X-ray analysis of different gypsum varieties is shown in FIGS. 1 to3. All patterns were recorded using an automatic powder diffractometer(Model APD 1700) from Philips, Kassel (DE). In all three Figures, therelative intensity of the reflections appears along the x axis and thediffraction angle (CuK_(o) radiation) along the y axis.

In FIG. 1 the reference symbol (1) represents the X-ray diffractionpattern of REA gypsum F (gypsum from the stack gas or flue gasdesulphurization plant of the Frauenaurach power station (DE)), whilethe X-ray diffraction pattern of calcium sulphate dihydrate (CaSO₄.2H₂O) is denoted by (2), that of calcium sulphate hemihydrate (CaSO₄. 1/2H₂O) by (3) and that of calcium sulphate anhydride (CaSO₄) by (4).

Accordingly, the X-ray diffraction pattern (5) of REA gypsum H (gypsumfrom the stack gas desulphurization plant of the Heilbronn power station(DE)) is shown in FIG. 2, the reference symbols (2), (3) and (4)relating to the various CaSO₄ types, as in FIG. 1.

FIG. 3 shows the X-ray diffraction pattern (6) of plaster of paris(stucco plaster) from Gebr. Knauf, Neuss works (DE), in comparison withthe abovementioned CaSO₄ types.

The results of the thermogravimetric analysis of different gypsumvarieties are shown in FIGS. 4 to 6. All analyses were carried out usinga simultaneous thermo-analysis apparatus (Model 409 C) from Netsch, Selb(DE). In FIGS. 4 to 6, the percentage by mass (left) and the degree ofheat in (μv) (right) are shown along the x axis, while the y axis showsthe temperature in °C. The curve (7) represents in each case thedifferential thermal analysis (DSC) and the curve (8) thethermogravimetry (TG).

FIG. 4 shows the thermogravimetric analysis of REA gypsum (flue gasdesulfurization gypsum) from the Frauenaurach power station. FIG. 5shows the thermogravimetric analysis of REA gypsum (flue gasdesulfurization gypsum) from the Heilbronn power station (in each casefrom the abovementioned stack gas desulphurization plant) and FIG. 6shows the thermogravimetric analysis of plaster of paris (stuccoplaster) from Gebr. Knauf, Neuss Works (DE).

Finally, FIG. 7 shows an apparatus for the preparation of halogen-freeand filler-containing, flame-retardant polyurea foam, in which gypsum(10) is fed from a container (9) via a motor-driven screw (11, 12) andthe flameproofing agent (13) from a container (14), likewise via amotor-driven screw (11', 12'), onto a further motor-driven screw (11",12"), and water and isocyanate prepolymer are added via metering units(15) and (16), respectively. The total mixture is then foamed in themould (17).

                                      TABLE 1                                     __________________________________________________________________________    Fire tests in accordance with DIN 53438, Part 2, on gypsum-filled             polyurea foams                                                                         . . . Parts of flue gas                                                                   . . . Parts of  ®Hostaflam                                                                 DIN 53438 - Flame application at                                              edge                                             desulfurization gypsum/100                                                                AP 462/100 parts of                                                                      Bulk density                                                                        mean flame height                       Example  parts of prepolymer                                                                       prepolymer (kg/m.sup.3)                                                                        (mm)     DIN 4102                       __________________________________________________________________________                                                   class*)                        1 (Comparison)                                                                         50          10         40    >150     B3                             2 (According to                                                                        50          15         38    135      B2                               the invention)                                                              3 (According to                                                                        50          20         40    130      B2                               the invention)                                                              4 (Comparison)                                                                         60          7.5        36    >150     B3                             5 (According to                                                                        60          10         42    120      B2                               the invention)                                                              6 (Comparison)                                                                         70          7.5        37    >150     B3                             7 (According to                                                                        70          10         45    120      B2                               the invention)                                                              8 (Comparison)                                                                         80          2.5        41    >150     B3                             9 (According to                                                                        80          5          41    110      B2                               the invention)                                                              10                                                                              (According to                                                                        100         2.5        47    140      B2                               the invention)                                                              11                                                                              (According to                                                                        100         5          43    110      B2                               the invention)                                                              12                                                                              (According to                                                                        100         5          43    100      B2                               the invention)                                                              13                                                                              (According to                                                                        110         2.5        47    140      B2                               the invention)                                                              14                                                                              (According to                                                                        120         2.5        49    140      B2                               the invention)                                                              __________________________________________________________________________     *) DIN 4102B1: "fire resistant                                                DIN 4102B2: "normally flammable                                               DIN 4102B3: "readily flammable                                           

                                      TABLE 2                                     __________________________________________________________________________    Fire tests in accordance with DIN 4102, Part 1, on gypsum-filled polyurea     foams                                                                                  . . . Parts of Flue                                                           gas desulfurization                                                                    Parts of  ®Hostaflam                                                                DIN 4102 Fire Shaft Test                                   gypsum/100 parts of                                                                    AP 462/100 parts of                                                                     Residual length.sup.1)                                                                Flue gas temperature.sup.2)               Example  prepolymer                                                                             prepolymer                                                                              (cm)    (*C)      DIN 4102 Class*)                __________________________________________________________________________    15                                                                              (According to                                                                        257      31        17      134       B1                                the invention)                                                              16                                                                              (According to                                                                        257      31        23      124       B1                                the invention)                                                              17                                                                              (According to                                                                        250      30        23      125       B1                                the invention)                                                              __________________________________________________________________________     *) DIN 4102B1: "fire resistant                                                DIN 4102B2: "normally flammable                                               DIN 4102B3: "readily flammable                                                1) Standard requirement: ≧15 cm                                        2) Standard requirement: ≦200° C.                          

We claim:
 1. A flame-resistant polyurea foam which- contains calciumsulfate dihydrate, - contains, as flame retardant, ammoniumpolyphosphate, - has a bulk density of from 25 to 250 kg/m³, - has anumber of open cells which is above 80% of all its cells, - comprisespolyurea which has been formed from a reaction of prepolymers ofdiphenylmethane 4,4'-diisocyanate with water.
 2. A polyurea foam asclaimed in claim 1, wherein said flame retardant is combined with afurther halogen-free flame retardant, a halogen-free synergist, or acombination thereof.
 3. A polyurea foam as claimed in claim 1, whereinsaid calcium sulfate dihydrate is natural gypsum or chemical gypsum. 4.A polyurea foam as claimed in claim 1, which contains, as flameretardant, a free-flowing, pulverulent ammonium polyphosphate of theformula (NH₄ PO₃)_(n) having n=20 to 1000 which is sparingly soluble inwater.
 5. A polyurea foam as claimed in claim 4, wherein, in saidformula (NH₄ PO₃)_(n), n is from 500 to
 1000. 6. A polyurea foam asclaimed in claim 4, wherein the ammonium polyphosphate ismicroencapsulated and contains from 5 to 25% by mass of awater-insoluble, synthetic resin which encloses the individual ammoniumpolyphosphate particles and which, optionally, has been cured.
 7. Apolyurea foam as claimed in claim 1, which has a bulk density of from 35to 90 kg/m³.
 8. A polyurea foam as claimed in claim 1, containing thefollowing components in % by mass:a) from 15 to 70% of polyurea, b) from25 to 80% of calcium sulfate dihydrate, c) from 1 to 15% of flameretardant, and, optionally, the following components in % by mass: d)from 0.1 to 5% of a fibrous filler, e) from 0.1 to 2% of catalysts basedon nitrogen compounds for the isocyanate/water reaction, f) from 0.1 to2% of foam stabilizers based on polysiloxanes, g) from 0.01 to 2% byweight of auxiliaries for dispersion and/or suspension and/or providingthixotropy.
 9. A polyurea foam as claimed in claim 8, wherein theamounts of said components a) through c) are as follows: a) from 20 to60%, b) from 30 to 70%, and c) from 2 to 10%, and, when said componentd) is present, the amount of component d) is from 0.2 to 2%.
 10. Aninsulating material comprising a polyurea foam as claimed in claim 1.11. An insulating material as claimed in claim 10, wherein said materialis in the form of a block foam or an on-site foam.